The present invention relates generally to position determining and display apparatus. More particularly, the present invention relates to a solid state system for digitally monitoring and sensing relative elevator car position and direction of travel.
In the prior art a great deal of position control technology has been suggested for monitoring and controlling elevator cars. The use of photo cells in elevator systems, broadly speaking, is well known. The concept is broadly depicted, for example, in U.S. Pat. No. 3,816,745 owned by the same assignee as in the instant case. A wide variety of previous designs have sensed elevator car position by reading perforated tapes and the like disposed in the conventional elevator hoistway. Some form of sensor apparatus may be employed for generating optical or electrical pulses as suitable sensors are moved relative to perforated tapes, vanes or the like.
U.S. Pat. No. 3,414,088 issued Dec. 30, 1968 employs a photocell system for detecting absolute car position through pre-punched tape coded with suitable "absolute position" indicating indicia. Caputo U.S. Pat. No. 4,019,606 discloses a system for determining through opto-electronics the position of an elevator car relative to a selected landing, wherein a photosensitive transistor senses light pulsed by a light emitting diode. U.S. Pat. No. 3,483,950 also discloses a photocell employed in a system for determining absolute position. U.S. Pat. No. 3,749,203 contemplates the use of perforated vanes through which light is passed periodically to determine absolute position. Similarly, U.S. Pat. No. 4,433,756 and U.S. Pat. No. Re. 27,185 also disclose complex absolute position monitoring apparatus wherein position is ascertained through optic readers employing elongated perforated tapes. U.S. Pat. No. 3,963,098 discloses a highly complex system for determining absolute position of an elevator car in response to the reading of a precoded tape. U.S. Pat. No. 3,773,146 discloses an electronic elevator position control device which monitors absolute position from data derived from predetermined elevator car positions.
Position sensing systems employing magnets are disclosed in U.S. Pat. No. 3,339,231. Savage in U.S. Pat. No. 3,856,116 includes an electro-mechanical device actuated by suitable cams for mechanically sensing absolute position. Magnetic position sensing systems are also disclosed in U.S. Pat. Nos. 3,048,818 and 3,199,630.
Most of the devices disclosed in the aforementioned patent references indicate elevator car position through relatively sophisticated display systems comprising a plurality of sequentially activated indicator lights or the like. However, in relatively recent years, partly because of aesthetics and "taste", architects, interior decorators, planners and the like have expressed a desire to deploy apparatus which emulates "old fashioned" position display systems. The older systems usually included a decorative cover plate provided with a plurality of suitable position calibrations. Usually a suitable pointer was employed to revolve relative to the cover plate in response to elevator car travel.
Thus a modern car position display system ornamentally reminiscent of the "old fashioned" variety is desirable. Of course it is further desirable to replace "multiple light" display systems without exchanging the originally installed elevator hoist control and travel apparatus, and without sacrificing reliability, dependability or speed. Therefore it is necessary to provide a highly reliable digital system for controlling an "antique" position display apparatus, incorporating all of the benefits of solid state technology.
Such a system must reliably operate within the extremely hostile environment of an elevator system. For example, the employment of digital control systems in the electrical environment of an elevator subjects the digital circuits to constant transients and spikes caused by the inductive nature of elevator motor technology. Moreover, it is desirable to provide a display system such as that of the present invention which may be retro-fitted to exist in systems without changing the complex and expensive elevator acceleration, deceleration and control apparatus already existing.